48. _C_ one time， Manchester was the home of the most productive cotton mills in the world. [at one time 曾经，一度]

　　A On B By C At D Of

　　49. _A_ it or not， his discovery has created a stir in scientific circles.

　　A Believe B To believe C Believing D Believed

　　believe it or not 信不信由你。 creat a stir 引起轰动。

　　50. Mr. Morgan can be very sad _C_， though in public he is extremely cheerful.

　　A by himself B in person C in private D as individual

　　in public 在公众面前; in private 私下单独一个人的时候。

　　第6课

　　关于逗号的一些知识

　　原则：逗号没有能力连接两个单独的句子。

　　如何区分短语与句子?一个结构如果有完整的谓语部分就是句子。

　　何为完整的谓语部分?如果能判断出一个结构的时态就可以称这个结构为完整的谓语部分。

　　在什么样的情况下一个逗号可以将句子分成两部分，而这两部分都有完整的谓语呢?

　　1 两个句子中间有连接词连接;

　　2 这两个句子是主从句关系(主从句之间一定要有句子引导词来引导)。

　　10. Walter offered us a lift when he was leaving the office， but our work _A_， we declined the offer. [declined v. 婉言谢绝]

　　A not being finished B not having finished

　　C had not been finished D was not finished

　　42. A survey was carrie3d out on the death rate of new-born babies in that region， _D_ were surprising. [survey 调查]

　　A as results B which results C the results of it D the results of which

　　51. All flights _D_ because of the snowstorm， many passengers could no nothing but take the train. [having been canceled 这里是独立主格作原因状语]

　　A had been canceled B have been canceled

　　C were canceled D having been canceled